Diabolik Lovers is definitely one of the hottest sexiest animes that I have ever seen. It is not hentai, but it is definitely in the smut category. At the same time, people who don't necessarily like smut, may still like this anime because of the supernatural paranormal themes, and the fact that no hanky panky actually occurs throughout the entire series.
It is because of the themes found in this anime, that it is so well-loved. There is a sexual theme; the male characters are all very attractive; there is a supernatural element, since the main male characters are vampires, and there is an English European vibe to the series. You see this in the way that the vampires speak, dress, look, and their gentlemanly behavior AT TIMES.
The Sakamaki's definitely treat poor Yui like food/cattle, but they also provide for her quite well, she is free to move around and go to school, and they do protect her. The behavior of the Sakamaki's seems so appropriate for European vampires, since they are the perfect mix of sexuality, propriety/manners, and indecency. It is all of this, that makes these vampires so appealing and attractive.
Though each episode of this anime is shorter than other animes, a lot does happen in each episode. There is a lot of hotness and sexuality present. So in this first episode, here are the hottest, sexiest moments.
When Yui first arrives at the Sakamaki mansion, the very first person she sees and speaks to is Ayato. Yui becomes scared because she realizes that Ayato doesn't have a heartbeat, so when he moves and starts speaking to her, she becomes nervous and shocked. Her fear seems to excite Ayato, so he tries to feed on her. Once he lays her down though to feed, Reiji ruins all of his fun. Reiji stops Ayato since he is traditional and feels that feeding so publicly is distasteful and impolite. This scene is quite hot though with Ayato licking Yui's neck; it is definitely a steamy moment 💚
Once everyone is assembled in the living room, they all talk together and try to figure out who Yui is and why she was sent to their mansion. During this time though, Kanato and Laito can't help but sample a taste of her. So Yui gets licked by these two very gorgeous men.